1. Optical Layer Protection Schemes
Layers within the optical layer
Optical channel (OCh) layer (path layer): end-to-end routing of the lightpaths
Optical multiplex section (OMS) layer (line layer): links between OLTs and OADMs
OCh layer protection schemes restore one lightpath at a time
Need demultiplex all wavelengths
OMS layer protection schemes restore the entire group of lightpaths on a link
Require less equipment

2. Optical Layer Protection Schemes
OLTs and OADMs can provide both OCh and OMS layer protection in linear or ring configurations
OXCs can provide OCh layer protection in linear, ring, and mesh configurations
Two choices for protection
Use unprotected WDM point-to-point systems and rely on OXCs to perform the protection functions (backbone networks)
Rely on the WDM line terminals and OADMs to perform the protection functions (metropolitan networks)

3. 1+1 OMS Protection
At one end, the composite WDM signal is bridged onto two diverse paths using an optical splitter
At the other end, an optical switch selects the better among the two signals

4. 1:1 OMS Protection
Use a switch at the transmitter, instead of a splitter
The composite WDM signal is transmitted over only the working fiber
If the working fiber is cut, the source and both ends switch over to the protection fiber
An APS protocol is needed
Benefits
Support low priority traffic on the protection fiber
Allow N working systems to share a single protection scheme

5. OMS-DPRing Dedicated protection ring
2 fibers, operate at the OMS layer
Each node transmits on both directions of the ring
Different nodes must transmit at different wavelengths
Normal operation: the ring functions as a bus, with one pair of amplifiers turned off and all the others turned on
When a link fails: the amplifiers next to the failed link are turned off and the ones that were originally inactive are turned on

6. OMS-SPRing
Shared protection ring with 4 fibers, analogous to a SONET BLSR/4
The two protection fibers do not have attached WDM equipment
Use either span switch or ring switch
Two-fiber version of OMS-SPRing
Dedicate half the wavelengths on each fiber for protection purposes
Make the protection wavelengths on one fiber correspond to the working wavelengths on the other fibersignals can be rerouted w/o requiring wavelength conversion

7. 1+1 OCh Dedicated Protection

8. Protection in SONET: Self-Healing Rings
A ring is the simplest topology that is 2-connectedresilient to failures
Much of the carrier infrastructure today uses SONET rings called self-healing rings
Can automatically detect failures and reroute traffic away from the failed links/nodes rapidly (within 60ms)
Three widely deployed ring architectures: UPSR, BLSR/4, BLSR/2
Unidirectional ring: carry working traffic in only one direction of the ring
Bidirectional ring: carry working traffic in both directions

9. Unidirectional Path-Switched Rings (UPSR)